In the past, it has been general that ultrasonic diagnostic apparatuses use an ultrasonic sensor with a piezoelectric element. However, with ultrasonic sensors using a piezoelectric element, there is a problem that it is difficult to produce two-dimensional (2D) sensors.
In order to obtain a three-dimensional (3D) image of good image quality in an ultrasonic diagnostic apparatus, it is desirable to use a 2D sensor that is able to acquire a 2D image without scanning a sensor array. Accordingly, there have been developed ultrasonic sensors of various structures based on various detection principles, other than those which use piezoelectric elements.
Among such sensors, the following one has been known as an ultrasonic sensor for detecting an ultrasonic wave by using an optical means (see Japanese patent application laid-open No. H10 (1998)-048039).
Japanese patent application laid-open No. H10 (1998)-048039 describes an ultrasonic sensor in which a refractive index in the interior of a ring resonator is changed due to the pressure of an ultrasonic wave received by the ring resonator. Specifically, when the refractive index in the interior of the ring resonator is changed, the resonance frequency of the ring resonator is changed, too, so the ultrasonic wave is intended to be detected by making use of the change in the resonance frequency.
As an imaging apparatus using an ultrasonic detecting device as stated above, there have been required ultrasonic sensors based on a variety of schemes from the viewpoint of further improvements in detection accuracy, the degree of freedom in design, and so on.